Fast hybrid automatic repeat request (HARQ) has been proposed as a vehicle to solve receiver memory problems which occur when soft combining schemes are used in wireless communications. The fast HARQ requires that an acknowledgement (or the so-called forward order) be transmitted within the next radio frame after the transmission of packet(s) in the forward direction. Hybrid ARQ (HARQ) is a link adaption technique used to improve the performance of wireless communications. In a Type 1 Hybrid ARQ, there is soft combining which is a type of repetition coding in which the retransmitted packet is combined with the initially transmitted packet. In Type 2 Hybrid ARQ, an incremental redundancy scheme is used. In both Type 1 and Type 2 Hybrid ARQ, the soft decision values of the erroneous packet, if detected, must be stored in the receiver which in turn can lead to very high memory requirements at the receiver. Thus the amount of memory required for storing these soft decisions is proportional to the retransmission time interval. Fast hybrid ARQ has been proposed to decrease retransmission delay which in turn decreases the memory requirements at the receiver.
In prior art schemes, the whole ARQ protocol is in the radio link control (RLC) layer and the feedback data as well as the retransmissions have been generated in the RLC layer as described in the Release 1999 3GPP specifications. This type of feedback data is not suitable for fast HARQ if the RLC in the network side is located in the radio network controller (RNC) since the Iub interface between RNC and Node B (the base station) can cause long delays. The delay of the Iub interface is one of the main reasons for the long round trip delays. This prior art technique requires that the retransmission delay becomes very high (typically from approximately ten to twenty transmissions in time intervals (TTIs). This retransmission delay therefore implies that the memory requirements at the transmitter, but especially in the receiver, must be very high in order to be able to retransmit and soft combine the retransmitted packets with the stored packets which were received erroneously.
One way to speed up the whole process is to generate the feedback data in the physical layer of the receiver. Similarly, the retransmissions should be generated at the physical layer of the transmitter. Alternatively, the feedback and the retransmission can also be generated in a layer which is co-located with: the physical layer, thereby eliminating any long delay between these two layers.
There are several ways of transmitting the feedback data. One possibility is to transmit it through existing uplink or downlink channel. This has the problem that the existing channels are usually terminated in the radio network controller (RNC) in the network side, i.e., thee is the delay between the base station and the RNC. Even if the termination of the existing transport channel were changed to a base station in the network side, the transmission delay would be at least three TTIs more than that of the proposed invention since the existing transport channels are interleaved at least over ten milliseconds (ms) (see 3GPP spec).
All the previous implies that a separate fast feedback channel needs to be defined. One straightforward possibility in a CDMA system is to transmit the feedback data using a separate code channel and transmit it in parallel with other data which has been proposed for instance by Motorola Corporation for its one XTREME system. This requires multi-code transmission which is not desirable in the mobile terminal (if the feedback is in the uplink direction).